Transparent sheets have been commonly used in copiers and printers to make imaged sheets for presentations. Most copiers or printers have optical sensing devices to detect the incoming sheets. However, transparent sheets can not be detected by optical sensors in these machines. In order to use transparent sheets in these machines, several methods have been employed to solve this problem.
One common used method is to adhere a piece of paper to a transparent sheet by a thin line of adhesive. After the transparent sheet is imaged, the operator has to remove the paper from the transparent sheet. However, the paper backing (usually 3 to 4 mil thick) insulates the transparency sheet from close contact with the heated fuser. This may result in insufficient heating of toners on the transparent sheet, and therefore also result in poor image quality.
The second method employed is to apply an opaque ink stripe along one edge of a transparent film as disclosed in U.S. Pat. 5,126,762. The opaque ink stripe allows the machines to determine the incoming transparent sheets, and overcome the problem of an insufficient heating of toners on the transparent sheet (film). But the ink stripes are not removable after imaging and leave visible marks during presentation.
The third method used is to employ a repositionable paper pressure sensitive adhesive (PSA) stripe onto one edge of the transparent sheet, wherein the operator peels off the paper PSA stripe from the transparent sheet after imaging. This allows for a full view of the imaged transparent sheet during the presentation. The paper PSA stripes are usually thick (2 to 4 mils). The edge portion of the transparent sheet with a paper PSA stripe is much thicker than the edge portion of the transparent sheet without the paper stripe. When a large number of sheets are put into a feeding tray, the thickness difference between the two edges of the transparent sheets results in a slope-like shape for the stack of transparent sheets. This limits the number of sheets which can be stacked at one time.
The fourth method is to use a thin plastic PSA stripe on the transparent sheets as disclosed in European patent EP 0 695 973 A1. The plastic PSA stripe article comprises an opaque coating (TiO.sub.2) on one side of a clear plastic stripe to render it the desirable opacity and an adhesive coating on the other side of the plastic stripe to give it the required adhesion to the transparent sheet. The plastic PSA stripes are much thinner than paper PSA stripes. With these stripes on the transparent sheets, many more sheets of transparent sheets can be stacked in the feeding tray of copiers and printers.
Each of the above methods serves its purpose. The thin plastic PSA stripe clearly is of advantage over paper PSA stripes. In the plastic PSA stripe disclosed in European patent EP 0 695 973 A1, opacity of the stripe is controlled by an opaque coating on the transparent plastic base stripe. The opaque coating should have sufficient thickness to give the desired opacity. This adds to the total thickness of the plastic adhesive stripe. It would be of-advantage to use an opaque plastic base stripe which will give the desired opacity. Also, it is found that the poor anti-static property of the plastic PSA stripes affects the feeding of the transparent sheets and causes jams of transparent sheets in a copier.
It has been found by the present inventor that transparent sheets bearing untreated plastic PSA stripes can be used in black and white copiers sometimes. However, they will jam in color copiers because they are exposed to a static environment in a color copier longer than they are in a black and white copier. It has also now been found by the present inventor that an anti-static coating on the opaque plastic stripes used on transparent sheets improved sheet feeding, while also increasing the number of sheets that can be stacked in a feeding tray at the same time. Furthermore, a rough anti-static coating gives the plastic PSA stripe the paper-like properties such as sufficient friction coefficient which will allow the machine to move the transparent sheet in and out of a copier or a printer. Likewise, though corona treatment can also generate an anti-static property on a polymeric plastic stripe, the present inventor has discovered that this kind of anti-static property will dissipate over time, thereby affecting the long term usefulness of the polymeric plastic PSA stripes on the transparent sheets.